Transformation of sound pressure level from the free field to the eardrum in the horizontal plane

TLDR

Measurements of sound‑pressure transformation, azimuthal dependence, interaural level difference, and ear‑canal pressure distribution from 12 studies are compiled into a common framework. The study proposes possible explanations for inter‑study differences. The authors compiled data from 100 subjects across five countries over 40 years and applied logical procedures to fit three‑dimensional distributions, producing sheets of sound‑pressure transformation, azimuthal dependence, and interaural difference across frequencies and azimuths. The analysis yields self‑consistent curves that describe the average sound‑pressure transformation from free field to eardrum across frequency and azimuth.

Abstract

Measurements of pressure transformation, azimuthal dependence, interaural level difference, and ear canal pressure distribution from 12 studies are brought together in a common framework. The pool of data covers 100 subjects, the majority male, measured in five countries over a 40-yr period. Logical procedures are developed to identify the surfaces which best fit these essentially three-dimensional distributions of data, making allowance for the many disparities between studies. Sheets of data are presented showing transformation to the eardrum, azimuthal dependence, and interaural difference as functions of frequency from 0.2 to 12 kHz at 45° intervals in azimuth. Other sheets show azimuthal dependence and interaural difference as functions of azimuth at 24 discrete frequencies. The logical procedures, data presentations, and review of disparities lead to the construction of self-consistent families of curves best fitting the data and showing the average sound pressure transformation from the free field to the human eardrum as a function of frequency at 15° intervals in azimuth. Possible explanations of differences between studies are suggested.